a) Field of the Invention
The present invention relates to a method for inducing desorption of hydrogen from a metal hydride containing the same, in which a non-thermal energy source is used to induce such desorption.
b) Brief description of the prior art
Metal hydrides are potentially ideal candidates for hydrogen storage and transportation. As hydrogen carriers, they provide high hydrogen storage capacities (up to for example 7.6 wt. % in Mg.sub.2 H.sub.2) and full safety. The safety is provided by endothermic reaction of hydrogen release, which excludes spontaneous (explosive) or uncontrolled reaction.
Metal hydrides are advantageous in that they can be handled and stored at ambient temperature without any atmosphere or pressure requirements. Such makes them economically favorable by elimination of cryogenic equipment necessary to use with liquid hydrogen or activated charcoal.
Metal hydrides are also very stable. Such is advantageous from a safety and economical point of view. However, because of their stability, most of the metal hydrides require elevated temperatures to initiate desorption.
Examples of metal hydrides having a high stability are MgH.sub.2 or Mg.sub.2 NiH.sub.4. They exhibit excellent hydrogen storage potential--with large hydrogen storage capacity (7.65 wt. % for MgH.sub.2 or 3.6 wt. % for Mg.sub.2 NiH.sub.4), low cost of the material and easy handling. However, desorption of hydrogen from these hydrides with reasonable kinetics requires heating to high temperatures: 350-400.degree. C. for MgH.sub.2 and 330-360.degree. C. for Mg.sub.2 NiH.sub.4.
For many applications, heating to such temperatures is disadvantageous. Indeed, it increases technical problems of hydrogen recovery and reduces effectiveness of the devices.
To solve this problem, it has already been suggested to reduce the stability of high temperature metal hydrides. Such may be obtained by alloying the metal hydrides with other elements. However, stability reduction occurs at the expense of the total hydrogen capacity.